The proposed studies have two major goals: (A) to improve neurological diagnosis of spinal cord injury by defining the sensory capacities that depend critically upon transmission along 3 major ascending pathways (in the ipsilateral dorsal column, the ipsilateral lateral column and the contralateral ventral quadrant), and (B) to improve understanding of the participation of spinal cord circuitries in the control or elimination of pain. This is a multidisciplinary approach within the neurosciences, involving highly quantitative evaluation of sensory thresholds and motor reactions to precisely controlled, somatosensory stimuli. A variety of correlations will be made between anatomical manipulations (and measurements) and the occurrence of functional deficits. Careful attention will be directed to the capacity for recovery of function following spinal lesions. Pharmacological compounds will be introduced directly on the spinal cord to determine the importance of different descending spinal pathways and transmitter systems for inhibition of pain. Clearly defining the roles of serotonin, noradrenalin and opiates on sensory coding and motor output at spinal levels is fundamental to understanding neural mechanisms of pain control, which should lead to new methods of pain therapy. The proposed studies will be conducted with monkeys, because the pain conduction systems are quite similar among primates and very different between primates and other mammals. The pain stimuli are brief, non-injurious and easily tolerated by monkeys and humans. Other stimuli will involve tactile and/or proprioceptive receptors and will test the most acuitive somatosensoty functions involved in active touch or grasp of objects in the environment. Sensations of texture or resistance to pressure by the hands are crucial to the advanced manipulative skills of primates, and the proposed studies will delineate the spinal pathways involved in these functions.